Electromagnetic transducer



Nov. 24, 1959 J. L. J. DONCEEL ETAL 2,914,621 ELECTROMAGNETIC TRANSDUCERFiled Aug. 29, 1957 Inventor J-L.J.:Doncee\ H.Vqn Ae r Merck A ttorne'y2,914,621 ELECTROMAGNETIC TRANSDUCER Jules Louis Joseph Donceel andHenri Cornelius Johannes van der Harck, Antwerp, Belgium, assignors toInternational Standard Electric Corporation, New York, N.Y., acorporation of Delaware Application August 29, 1957, Serial No. 681,018

Claims priority, application Netherlands September 5, 1956 1 Claim. (Cl.179-1002) The invention relates to an electromagnetic transducer ormagnetic head designed to permit recording on a magnetic member such astape or drum, and also to permit the reading of information previouslyrecorded on such member.

This invention relates particularly to magnetic heads using a magneticcore made of a single magnetic member shaped as a ribbon (at least inthe vicinity of the record medium) and bent in the form of a partiallyclosed loop, the ends of the ribbon defining a non-magnetic gap. One ormore coils are mounted on the ribbon, and the whole assembly is mountedin a non-magentic housing.

Such magnetic heads are described in the US. Patent Nos. 2,469,444 and2,674,031 as well as in Belgium Patent No. 525,092.

A general object of the invention is to provide a magnetic head of theabove type which is particularly adapted to being produced in largequantities and within given tolerances.

Another object of the invention is to provide such a magnetic headassembly having an overall thickness approximating the width of themagnetic ribbon.

Another object of the invention is to provide a magnetic head assemblyadapted for use as an interchangeable unit for a multiple head assemblycomposed of several such untis closely stacked together.

Another object of the invention is to provide a magnetic head assemblyincluding a separate sub-assembly for terminal strips to be lodged inthe main housing.

In accordance with the invention, an electromagnetic transducer, ormagnetic head, comprises a magnetic core such as a thin ribbon bent intoa partially closed loop with the flat ends thereof separated by a narrownonmagnetic gap, a coil, or coils, mounted on said ribbon, anon-magnetic housing for said ribbon(s) and coil(s) adapted to squeezesaid ribbon ends together and ground and/or lapped next to said ribbonends to adjust their separation to the desired value. I

In accordance with an aspect of the invention the housing is in the formof a thin non-magnetic block provided with a recess, adapted to housethe whole of said ribbon, and terminating as a slot of a depth equal tothe width of the ribbon and adapted to house the ends thereof. Thecentral part of the recess houses the coils mounted around the ribbonand the remaining part of the recess houses an insulated flat terminalstrip having a thickness equal to the width of said ribbon. The terminalstrip is fixed to the housing and is formed of two layers with insiderecesses adapted to sandwich securely the external electrical terminals,on which the ends of the thin coil wires are attached. An insulated coreformer member is squeezed inside the loop so as to press firmly the endsof the loop on the inside of the slot and the opposite central part ofthe loop against the inside edge of the terminal strip.

Although U.S. Patent No. 2,469,444 discloses a housgap.

ing in the form of a cup-shaped receptacle for the ribbon, constitutingthe core of the head, the latter is only fixed in said housing at theproximity of the non-magnetic gap. This applies also to the arrangementdisclosed in the Belgian Patent No. 525,092. In the US. Patent No;2,674,031 the mounting block used also houses the ribbon core memberonly in the vicinity of the non-magnetic In this latter mentionedpatent, means are also disclosed for holding the external electricalterminals, but these are secured with the help of the coil formers. Inthe same patent, a ceramic core former is secured to the block by meansof a ceramic pin. Finally, in US. Patent No. 2,662,120, not previouslymentioned, but relating to magnetic heads using laminae, a core formeris not used but a spring external to the core configuration is designedto place the latter into position.

In accordance with another feature of the invention, an electromagnetictransducer or magnetic head as described above, is further characterizedin that the part of the recess designed to house the coils extendsthrough the block, whereby the openings provided house not only thecoils of the head mounted in the block but also, in the case of aplurality of closely stacked heads, the protruding part of the coils ofthe head mounted in the next block.

The multiple magnetic heads adapted for simultaneous multi-channeloperation are in themselves known from US. Patent 2,751,440. In thatpatent a construction consisting of a plurality of thin stacked singlechannel units which are complete in themselves is disclosed. Thedisclosed units carry their own terminals and are interchangeable withina particular multiple head.

The above-mentioned and other features and objects of this inventionwill become apparent by reference to the following description taken inconjunction with the accompanying drawings, wherein:

Fig. 1 is an elevation view of the magnetic core and of the coils usedin the magnetic head of the invention;

Fig. 2 is an end elevation view of the structure shown in Fig. 1;

Fig. 3 is an exploded view of the terminal strip arrangement for themagnetic head of the invention;

Fig. 4 is a perspective view of the main mounting block designed tohouse both the structure of Figs. 1, 2, and 3; and

Fig. 5 is an elevation view of the complete magnetic head assembly.

Referring to Figs. 1 and 2, the magnetic circuit comprises a magneticcore 1 which may be in the form of a ribbon having a thickness of theorder of 0.2 mm. and a width of the order of 1.2 mm. This ribbon is madeof high permeability magnetic material such as Permalloy. As shown, theribbon 1 is bent in the form of a closed loop, right angle folds beingprovided at 2 and 2, and oblique folds at 3 and 3, the two ends of theribbon merging together at 4 to form a tail 5. This tail 5 is useful inmounting the magnetic circuit on the mounting plate shown in Fig. 4 andwhich will be described later. Although a ribbon with a rectangularcross section is shown, another cross-section, e.g. round, might beused, provided the ends of the magnetic core are flattened in the zonewhich will define the nonmagnetic gap.

Two coils 6 and 6', including their formers, may he slipped onrespective legs of the ribbon 1 as shown.

The assembly of the coils and of the core may be made in various ways.The ribbon may initially be bent at 2 and 2' only, this operation beingfollowed by 'slipping of the formed coils on the respective legs, andthen shaping the tail of the ribbon as shown in Fig. 1,

Alternatively, the ribbon 1 in its initial straight shape may be foldedon itself at its middle to constitute the tail 5, this operation beingfollowed by the separation of the two legs at 4, by bending at 3 and 3',by slipping the formed coils on the respective legs and by bending at 2and 2, the length of the ribbon being sufli cient to ensure an overlapof the two ends between 2 and 2'. The overlapping ends may then besqueezed together with the help of a small connecting part enclosing theoverlapping ends of the ribbon to secure a low reluctance joint.

Alternatively, one may start with the ribbon in two separate parts, onefor mounting each coil, all the bends shown in Fig. 1 except those at 2and 2 being already made before the formed coils are slipped on therespective legs. This operation is then followed by bending at 2 and 2'and the overlapping ends may be joined as explained before. If desired,one can also use this last method including the additional step ofbending at 2 and 2 previous to the mounting of the coils which wouldthen have to be wound on the respective legs, a central joint to unitethe ends of the ribbon being made as before. The provision of all thefolds previous to the mounting of the coils has of course the advantageof avoiding bending the magnetic ribbon after annealing.

The first sub-assembly of the core and the coils having been explained,the second sub-assembly constituted by the terminal strip as shown inFig. 3 will now be described. A lower plate 7 with a central hole 8. isprovided with two recesses 9 and 9' shaped as shown. An upper plate It}is also provided with a central hole 11 and with recesses 12 and 12'substantially corresponding to those in the lower plate. Both plates aremade of insulating material and are designed to enclose the externalelectrical terminals 13 and 13' which are pieces of wire each bent atone of its ends, these bent ends being flattened at 14 and 14 into ashape adapted to fit into the central part of the recesses 9 and 9.Through the grooves 15 and 15 respectively, the ends 16 and 16' of thecoils shown in Fig. 1 are inserted. In this manner, the very thin wireforming the coils and which is quite fragile may be secured to theexternal terminals. After connecting the ends of the coils to the ends14 and 14' of the terminals, the latter will be firmly clamped insidethe terminal strips by pressing together the lower and upper plates. Theplates may be pressed together by a screw 17 extending through holes-11and 8 designed also to attach the terminal strip sub-assembly to themain base plate.

The base plate is shown at 18 in Fig. 4. Apart from two holes 19 and 19'used in the assembly of several such base plates the central portion isrecessed at 20 as shown. The recess 2% is designed to accommodate theterminal strip sub-assembly, the screw 17 engaging a tapped hole 22.Base plate 18 is made of nonmagnetic material such as brass and thenarrowing part 23 of the recess, terminating into a slot 24, houses thetail 5 (Fig. l) of the magnetic ribbon. At 25 and 25', the recessextends through the base plate 18 to provide sufiicient space forstacked formed coils where several magnetic head assemblies are combinedalong a direction parallel to the axis of the hole such as 19.Independently of the use of one or more magnetic head assemblies, theholes such as 19 may always serve to mount the assembly on any suitablesupport.

Fig. 5 shows the complete assembly of the parts already described withthe help of the previous figures. The hole it through which passes thescren 17 is preferahly bored to permit the head of this screw to beflush with the upper face of the base plate 28 so that adjacent unitsmay be pressed-against one another.

T he construction described lends itself to high manufacturin-gprecision of the order of 0.005 mm. by using precision jigs.

Mounting of the various elements is preferably made in the followingmanner. Before mounting the core and coil assembly shown in Fig. 1 onthe base plate 18, an insulating core former 26 is properly positionedas shown in Fig. 5. This core former 26 closely bears upon the magneticribbon. l and particularly against the central part thereof. In Fig. 5,the ribbon core 1 is shown to have been made out of two parts with theends between the bends 2 and 2' overlapping onean other and enclosed bya joining member 27. The member 2.7 is in the form of a small piece ofribbon material bent on itself so as to enclose the overlapping parts ofthe ribbon core. At its opposite end, the core former 26 is shaped at 28so as to closely contact the parts of the magnetic ribbon ending intothe tail 5'. The core former 26 is provided with a thin groove 29through which the part of the windingwire joining the two coils 6 and 6'may be inserted. The core former 26 is surrounded by a very thin ribbonof insulating material 30 which terminates into a tail 31 projectingsomewhat beyond the tail 5 of the ribbon core. This permits a doublethickness of thin insulation material to separate the parallel parts ofthe magnetic tail 5. Thus, provided with its former, the coil and coresub-assembly may be inserted in the recess provided in the base plate18' with the tail 5 fully inserted into the slot 24. The terminal stripmay now be mounted as shown so as to rigidly define the position of thecore and coil subassembly.

A multiple head arrangement may be produced by stacking the assembliesin alignment. Due to the openings 2S and 25 the coils 6 and 6' projectsomewhat above the upper plane of the base plate 18. This is due to themagnetic core ribbon-having a width exactly equal to the depth of themain recess. Thus, the coils extend into the corresponding. openings ofthe next head unit which is directly on top of the head considered.

A single or a multiple magnetic head unit having thus been obtained,plastic material may be used to fill the spaces on the central-recess2%, by means of the openings 25 and 25' which will afford throughchannels in the case of a multiple unit. The single multiple assemblymay then have its straight edge 32 transformed into the slightly curvededge 32' by a grinding or lapping process. The width of the gap 33 maythus be adjusted to the required value, the tail 5 being cut ofi in thisprocess.

An improved anchoring of the external terminals 13 and 1-3 may beobtained by applying a coating 34 of hard glue in the Zone surroundingthe openings in the terminal strip sub-assembly through which theseexternal terminals project.

While the principles of the invention have been described above inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationon the scope of the invention.

What is claimed is:

An electromagnetic transducer comprising a magnetic core in the form ofa ribbon, said ribbon being arranged to define a loop, the ends thereofbeing fiat, and the flat portions being oppositely disposed andseparated to define a predetermined narrow non-magnetic gap, a pair ofcoils mounted on opposite legs of said loop, a non-magnetic housing forsaid ribbon and coils adapted to maintain said. ribbon ends in givenspatial relationship, characterized in that said housing'is' in the formof a thin block and is provided with a recess having a pair of oppositewalls symmetrically inclined toward an edge of said block, the inclinedwalls terminating at the edge to define a narrow slot, said ribbon endsbeing snugly mounted in said slot, said coils being mounted in thecentral part of said recess, an insulated terminal strip havingthickness approximately equal to the width of said ribbon, fixed to saidhousing in the remaining part of said recess, a pair of electricalterminals mounted to said strip, means connecting the ends of the coilwires to said terminals, an insulated core former member mounted snuglyinto said loop and shaped to press the ends of said loop against saidinclined walls and to press the opposite central part of said 100pagainst the inside edge of said terminal strip, and the peripheral edgesof said insulating core former being surrounded by a thin strip ofinsulating material with the ends thereof extending between saidopposing flat ends of said ribbon, thereby determining the separationbetween said ribbon ends.

References Cited in the file of this patent UNITED STATES PATENTSBuhrendorf Apr. 15, 1952 Bauer Sept. 1, 1953 Holmes Nov. 3, 1953 MunroFeb. 9, 1954 Buhrendorf Apr. 6, 1954 Zenel Feb. 14, 1956

